Making low-alloy high-strength steel of the copper-phosphorussilicon-chromium type



Patented June 10, 1941 MAKING LOW ALLOY HIGH STRENGTH STEEL OF THE COPPER-PHOSPHORUS- SILICON-CHROMIUM TYPE Clarence D. King, Mount Lebanon, Pa., assignor to United States Steel Corporation of Delaware, a corporation of Delaware No Drawing. Application September 10, 1940, Serial No. 356,222

2 Claims.

This invention is a method of making low-alloy high-strength steel of the copper-phosphorus silicon-chromium type.

Steel of the above type contains not more than .10% carbon, from .20% to .50% copper, from .10% to .50% manganese, from .10% to .16% phosphorus, not more than .05% sulphur, from .50% to 1.50% silicon and from .50% to 1.50% chromium. Its features need not be discussed since they are described by current publications.

In making this type of steel it is necessary to convert a ferrous charge to a molten steel of sufficiently low carbon content to permit the addition of suflicient ferrophosphorus or other phosphorus bearing material, ferrochromium, ferromanganese and ferrosilicon to provide it with the described percentages of the metallic constituents of these alloys without raising its carbon content above the .10% maximum, it being remembered that all of these ferroalloys contain carbon that is added to the steel. The described percentage of copper may be added to either the charge or the steel at any time and presents no problem in so far as the present invention is concerned, as will presently be realized. The sulphur content of the steel is residual.

When these ferroalloys are added to the steel of the described low carbon content, the steel normally does not recover all of the available alloy constituents, the percentage of the available alloy constituent recovered being called the alloy efficiency of the addition containing that constituent. When the alloy efliciency of a ferroalloy addition is low, it is necessary to add larger amounts of that ferroalloy which, incidentally, adds proportionally larger amounts of carbon and consequently necessitates the production of a steel of lower carbon content than would be necessary if the alloy efliciency were higher. Of more importance is the fact that certain of the ferroalloys, notably ferrochromium, are expensive, it following that it is particularly desirable to obtain the highest possible alloy efliciencies when they are added to the steel.

The object of this invention is to make steel of the type under discussion so as to obtain the highest possible alloy efiiciencies when the necessary ferroalloy additions are made and, because of its high cost, most particularly when the ferrochromium is added. It can now be understood why this invention is not concerned with the addition of the copper necessary to produce this steel type,

it being well known that copper additions result in alloy deficiencies approaching 100%.

According to this invention, the described type of steel is made by converting a ferrous charge containing at least .10% phosphorus by the acid Bessemer process to a Bessemer steel containing at least .10% phosphorus and then adding the necessary ferroalloys to this Bessemer steel other than ferrophosphorus in amounts providing it with the alloy contents characteristic of the described type of steel, the carbon content of this Bessemer steel being dropped sufliciently low during its conversion to permit the addition of these necessary ferroalloys without raising its carbon content above .10%. The ferroalloys mentioned are added after the steel has been converted to a Bessemer steel of the described low carbon content, the steels phosphorus content of at least .10% functioning to efiectively increase the alloy efiiciencies obtained and, most particularly, to

increase the alloy efliciency obtained when the ferrochromium is added. Chromium alloy efficiencies of and up are obtained when the foregoing is followed.

The ferrous charge previously mentioned may .be of the same character with which an acid Bessemer converter is normally charged excepting that its composition. is adjusted to include at least .10% phosphorus. Depending on the phosphorus content required by the composition of the finished steel, the charge may contain a higher amount of phosphorus up to .16%, all of the phosphorus added the charge being recovered. However, phosphorus may be added to the converted steel if desired.

As a preferred practice, conversion of the ferrous charge by the acid Bessemer process is carried out so as to produce a Bessemer steel containing not more than .04% carbon and at least .10% phosphorus. After conversion, the copper and any additional phosphorus necessary is added to the steel while it is in the Bessemer vessel, the steel then being poured in a ladle and ferrochromium, ferromanganese and ferrosilicon added as required. The copper and phosphorus are added in amounts providing the steel with a copper content of from 20% to .50% and a phosphorus content of from the described .10%. up to .16%. The other additions are made in amounts respectively providing the steel with a chromium content of from .50% to 1.50%, a manganese content of from .10% to .50% and a silicon content of from .50% to 1.50%. The sulphur maximum is inherent, it being prevented from exceeding .05% by proper selection of materials constituting the ferrous charge converted.

As previously indicated, unusually high alloy efliciencies are obtained at the time the ferrochromium, ferromanganese and ferrosilicon are added, and all of the phosphorus is recovered. However, stress is laid on the 95% and up alloy efiiciency obtained when the ferrochromium is added because of the cost of this material and, also, because many unsuccessful efforts have been made by others to approach this high chromium alloy efliciency. High alloy efficiencies in all instances contribute toward decreasing the cost of making the type of steel with which this invention is concerned.

This is a continuation-in-part of my application entitled Method of making high phosphorus corrosion resistant iron and steel alloys, filed July 26, 1938, and bearing Serial No. 221,441.

I claim:

1. A method of making low-alloy high-strength steel of the copper-phosphorus-silicon-chromium type containing not more than .10% carbon and at least .10% phosphorus, said method being characterized by converting a ferrous charge containing at least .10% phosphorus by the acid Bessemer process to a Bessemer steel containing at least .10% phosphorus and adding suflicient ferrochromium to said Bessemer steel to provide it with the chromium content characteristic of said type, the carbon content of said Bessemer steel being adjusted during said conversion sufficiently low to permit adding said ferroch omium and any other material necessary to adjust its composition to that characteristic of said type without raising its carbon content above .10%, said phosphorus content of said Bessemer steel efl'ectively increasing the alloy efliciency obtained from adding said ferrochromium 2. A method of making a low-alloy highstrength steel of the copper-phosphorus-siliconchromium type, said method including converting a ferrous charge containing at least .10% phosphorus by the acid Bessemer process to a Bessemer steel containing not more than .04%

carbon and at least .10% phosphorus, adding copper and any necessary additional phosphorus to either said charge or said Bessemer steel to provide the latter with a copper content of from 20% to and a phosphorus content of from said .10% up to .16%, adding ferrochromium, ferromanganese and ferrosilicon to said Bessemer steel in amounts providing it with a chromium content of from .50% to 1.50%, a manganese content of from .10% to .50% and a silicon content of from 50% to 1.50%, and processing said Bessemer steel to a. low-alloy high-strength steel of said type, said phosphorus content of at least .10% in said Bessemer steel efiectively increasing the alloy efliciencies obtained when adding said ferroalloys.

CLARENCE D. KING. 

